The present invention relates to an optical pickup device and also an optical disc apparatus.
As the background art of a field of the present technology is already known Japanese Patent Laying-Open No. 2006-344344 (Patent Document 1). In this Patent Document 1 is described, as the problem to be dissolved, “Obtaining a desired signal from an optical disc having plural numbers of recording layers, at high accuracy”, and as the means for dissolving, there is described, “A light flux of P-polarization emitting from a light source unit 51 is reflected on a optical disc 15, and enters into a lens 61 while becoming the S-polarization light. And, on quarter wave plates 62 and 63, each is given with an optical phase difference of +¼ wavelength to the light flux entering into +X side of an optical axis, and is given with an optical phase difference of −¼ wavelength to the light flux entering into −X side thereof. With this, a signal light passing through the quarter wave plate 64 comes into the S-polarization, while a stray light comes into the P-polarization, and on a polarization optical element 64, only the signal light can pass therethrough.”
Also, for example, in Non-Patent Document 1 is described, as the problem to be dissolve, “When recording/reproducing a dual layer disc, in particular, if a light reflecting from a layer differing from a target layer enters into a photo detector, as a stray light from other layer(s), an offset is generated on a TE signal. For this reason, with the conventional structure without a countermeasure for the stray light from other layer (s), the offset of the TE signal on the dual layer disc comes to be large, comparing to that in the case of a single layer, and therefore a stable control is prevented”, and as the dissolving means, there is described, “The photo detector for use of tracking is disposed in a region where no stray light enters.” The structures of that are described is also described in Japanese Patent Laying-Open No. 2004-281026 (Patent Document 2).